#
# READEM File for the August and November 2014 SPT-GMOS Data Release 
#
# When using any of the data downloaded from this archive, it is appropriate 
# to cite Ruel et al. (2014 - ApJ 792, 45) and Bayliss et al. (2014 - AAS 
# Meeting #224, #405.07). A paper dedicated to describing these reductions 
# and the resulting data in more more detail is also formcoming (Bayliss et 
# al, in prep).
#
#
# Please direct any questions/concerns to Matthew Bayliss via email 
# at mbayliss@cfa.harvard.edu

I. Description of the different kinds of files that are available in this 
    archive.

  1) Reduced optical imaging. These images where obtained with a variety of 
      different facilities as a part of and ongoing follow-up program to 
      obtain imaging in several optical bands at the positions of galaxy 
      cluster candidates that were identified in South Pole Telescope 
      mm-wave survey data. See Bleem et al. (2014 - submitted to ApJ) for 
      details regarding this imaging followup. The imaging bands and depth 
      of this imaging can vary significantly from cluster to cluster, and 
      in some cases there is additional Gemini-GMOS preimaging available 
      (see the 2011 data release, or simply query the Gemini archive at the 
      CADC - http://www2.cadc-ccda.hia-iha.nrc-cnrc.gc.ca/en/gsa/)

# The placeholder reference for optical follow-up of SPT clusters is Song 
# et al. (2012 - ApJ 761, 22), but this reference becomes obsolete once 
# Bleem et al. is available.


  2) Reduced 2-dimensional spectra from GMOS multi-slit masks. These files have 
      been run through the Gemini IRAF software package that is provided by the 
      Gemini observatory (e.g., http://www.gemini.edu/node/10795). These 
      reductions include bias corrections, wavelength solutions, low-order 
      flat-field corrections, and simplistic sky-subtraction. In some 
      cases we have also performed a preliminary processing pass on these data 
      using custom IDL codes designed to provide improved sky subtraction and 
      cosmic ray rejection. For the most part these data *have not been processed 
      in an optimal way*, and there is significant room for improvement in the 
      reduction of data from some masks. Future data releases will provide updated 
      reductions as they become finalized. Due to extreme fringing at wavelengths 
      redward of ~7000 angstroms, spectra that were not taken in nod-and-shuffle 
      mode are particulary messy in the red.

  3) Extracted 1-dimensional spectra. These extractions were made using custom 
      code that identifies sources along the spatial axis of each slit. 

        A. These files are in the .fits format with multiple extensions. The first 
            extension a 1-D array of flux values, the second extension is a 1-D 
            array of flux uncertainty values, and the third extension is a 1-D array 
            of wavelength values for the center of the wavelengths bins into which 
            the flux and uncertainties were extracted.

        B. We have also applied a flux calibration to the extracted spectra based on 
            archival Gemini-South/GMOS observations of the standard star LTT 1788. 
            This flux calibration is approximate, but provides a reasonable 
            "flattening" of the final 1D spectra in most cases. The absolute calibration 
            offset (i.e., zero point) is highly uncertain, as this can vary strongly as 
            a function of several factors, such as weather conditions and how recently 
            the telescope mirrors have been cleaned and re-surfaced. So with these 
            significant caveats regarding the absolute flux calibration, the final 
            calibrated spectra are in units of f_lambda, 1e-16 erg s^-1 cm^-2 A^-1.

  4) Redshift catalogs.

      A. These are ascii files -- one for each spectroscopic mask -- 
          that contain the measured redshifts for the large majority of the reduced 
          spectra described in (2 and (3 above. The catalogs contain six columns:

      (1)             (2)         (3)        (4)        (5)            (6)
SPT Candiate Name   Galaxy Name   Slit RA   Slit Dec    redshift  redshift uncertainty


      B. The "Slit RA" and "Slit Dec" fields are the centroids of the slitlets from which 
          the galaxy redshift was measured. This is generally identical to the RA and Dec 
          of the object placed in each slit based on the imaging described in (1 above. 
          There are, however, rare exceptions when there were slits that produced mutliple 
          spectroscopic traces (i.e., one or more sources *other* than the primary object 
          placed in the slit fell serendipitously into the slit and produced a strong 
          trace, which was then extracted). Future data releases will include updated 
          coordinates for these rare cases, but that is currently work-in-progress.

      C.  The redshifts provided in these catalogs were measured by cross-correlating 
          strong features in the data against the common features that appear in galaxy 
          spectra. The dominant features used typically included the Ca H&K doublet, the 
          hydrogren Balmer series (esp. H-beta, H-gamma, and H-delta), the Fraunhofer G-band 
          complex, and forbidden emission lines when available (almost exclusively [O II] 
          3727/3729, [Ne III] 3863, and [O III] 4960/5008). The redshifts presented here 
          represent a somewhat conservative list, and are not necessarily exhaustive in 
          terms of the maximum number of redshifts that may be recoverable from the 
          spectra. They should, however, represent the vast majority of measurable redshifts 
          from the GMOS spectra.

  5) Mask Defintion Files (MDFs). These are fits table format files that contain all 
      of the information that describes the GMOS multi-slit masks that were used to 
      obtain the spectroscopic data provided here. These files would be useful, for 
      instance, in combination with the available imaging data described in (1 above, 
      for identifying the positions of the galaxies that are responsible for the 
      serendipitous additional spectroscopic traces that appear in some of the 
      slitlets (see the discussion in 4-A above).


II. Description of File naming conventions.


    1) All filenames include a string that denotes the name of the relevant original SPT 
        galaxy cluster candidate. SPT candidate names have one of two formats: either 
        SPT-CLJXXXX-YYYY, sptcljXXXX-YYYY, or sptclXXXX_YYYY, where "XXXX" and "YYYY" are the 
        sexagesimal Hours and Minutes (RA) and Degrees and Arcminutes (Dec), respectively, 
        of the candidate's astrometric coordinates. The one caveat here is that some of 
        the proprietary (i.e., non-GMOS) imaging that has been uploaded dates far enough 
        back that these files have names what were generated with a different 
        truncation/rounding scheme. This said, it shoudl always be clear which imaging 
        files match up to the other files because any differences will be at most one 
        minute/arcminute in RA/Dec. 

    2) The .fits files containing individual 1D spectra also contain strings that indicate 
        the custom multislit spectroscopic mask from whch each spectrum originated. These 
        strings are of the format, NNn[C or Q]PPmZZ, where "NNn" indicates the semester 
        during which that the mask was designed (e.g., "11a" for the 2011A semester, or 
        "13b" for the 2013B semester), [C or Q] indicates a single string character that 
        will be set to either "C" or "Q" depending on whether the Gemini program in that 
        semester was executed in either classical (C) or queue (Q) mode, "PP" indicates 
        the Gemini program number in the semester of observation (always an integer, e.g., 
        "04" or "72"), "m" is always the single string character, "m", and "ZZ" indicates 
        the mask number in the semester during which the mask was designed (also always an 
        integer, e.g., "01" or "16").

    3) The .fits files containing the reduced 2D spectra include the SPT cluster candidate 
        string, always followed by "_2D.m", and then by a string of the format "ZZz" where 
        ZZ is the same mask number described in (2 above, and the "z" character is a string 
        with value "a", "b", "c", "d", "e", etc, that indicates individual spectroscopic 
        exposures taken with that mask (1D spectra are extracted from individual 2D spectral 
        data and then coadded).


    4) The ASCII files that contain the redshift catalogs resulting from the GMOS spectra 
        have the format sptcljXXXX-YYYY.catalogs, where the "XXXX" and "YYYY" strings are 
        identical to those described in 1) above. 

    5) The Mask Definition Files (MDFs) are in the same filename format that they have on 
        the Gemini CADC archive, e.g., "GS2012AQ037-10.fits" is mask number 10 from the 
        queue program number 037 during the 2012A semester.

